1. Field of the Invention
The invention is directed to a method for optimization of transmission links in a cellular telecommunications network.
2. Description of the Related Art
FIG. 1 shows an example of a situation which sometimes occurs during a hard handover, i.e., when a mobile station 10 changes the base station or base stations 20 it is presently using. Such a situation may occur, for example, when a mobile station moves from one cell to another in a cellular telecommunication system. FIG. 1 depicts two situations, situation A, when the mobile station 10 is still in the area of the first cell, and situation B, when the mobile station (MS) has moved to the area of the second cell. FIG. 1 shows also base stations (BS) 20, which are controlled by radio network controllers (RNC) 30, 31. The radio network controllers are connected to a mobile switching center (MSC) 40. In the first situation, the mobile station 10 is in position marked by the letter A, having connections to base stations 20 controlled by the first RNC 30. The radio network controller 30 comprises combining 33 and splitting 34 units. Combining units 33 combine uplink signals belonging to same bearer coming from base stations, and splitting units replicate downlink signals to more than one base station. The RNC 30 also comprises a protocol control block 32, which executes the protocols needed for communication with the mobile station 10. The RNC 30 forwards the uplink data to and receives downlink data from the MSC 40, which communicates with the rest of the telecommunications network.
When the mobile station moves to the position marked by the letter B, the mobile station 10 establishes radio links to the base stations 20. During the handover signaling, the first RNC 30, i.e., RNC1 in FIG. 1, establishes the necessary connections B′ via RNC2 to base stations 20 controlled by RNC2, and releases the former connections A′ to the base stations 20 controlled by RNC1. The controlling RNC, i.e., RNC1 in FIG. 1, is commonly called the controlling RNC. The other RNC, i.e., RNC2 in FIG. 1, is commonly called the drift RNC. Further, in some specifications for the UMTS (Universal Mobile Telecommunication System), the interface between two RNCs is called the lur interface, and the interface between a MSC and a RNC is called the lu interface. These interface names are used in this specification.
The system of FIG. 1, namely the use of a controlling RNC and a drift RNC, has certain drawbacks which arise from the fact that in situation B the transmission links are routed via two RNCs, instead of only one as in situation A. As the number of transmission links increase, the delays created by the links also increase. The increase of delays places more demands on the whole network, when the network has to fulfill strict delay requirements for constant delay services, such as speech. Further, since the number of transmission links in use increases, the load on the network increases.